Imaging apparatus and camera system

ABSTRACT

An imaging apparatus includes an optical system including a focus lens, a driver configured to drive the focus lens, a controller configured to control a supply of power to the driver, and a setting unit configured to set a power supply mode for specifying a method of supplying power to the driver. When a predetermined power supply mode is set, the controller determines according to a magnitude of a depth of field of the optical system during whether holding power for holding the state of the focus lens is supplied to the driver when the focus lens is stopped, and controls the supply of the holding power to the driver according to the result of the determination.

BACKGROUND

1. Technical Field

The technical field relates to an imaging apparatus, such as a digitalstill camera or a digital video camera, having drive unit that can drivea focus lens.

2. Related Art

A conventional digital camera includes a motor (actuator) for driving azoom lens, a focus lens, a diaphragm, or the like (see, for example,JP-A-2008-92619). For the digital camera described above, variousproposals are provided, such as improvement of drive noises of themotor, the maximum operation speed, precision at a stop position, powerconsumption, or the like.

In order to save power consumption of the digital still camera, it canbe considered not to supply power to a motor that is not being driven.However, when no power is supplied to a motor mounted in a normaldigital camera, the motor cannot allow a rotor to stop at a desiredposition accurately, so that a lens or the like cannot be controlled ata desired position. This will be detailed below with a stepping motortaken as an example.

FIGS. 12A and 12B are sectional views of a stepping motor. The steppingmotor includes a rotor 10 made of a magnet and a stator 20 provided withan electromagnet. The stepping motor rotates the rotor 10 by attractionforce caused between the magnet of the rotor 10 and magnetic field whichis generated by an electric current flowing through a stator winding 22.

A stepping motor that drives a movable lens with a micro-step drive doesnot turn on and off a conduction of electric current to the statorwinding 22 simply, but controls finely the ratio of the electric currentflowing through the adjacent two windings, so that the position of therotor 10 is controlled finely. Therefore, when no current is supplied tothe stator winding 22 of the stepping motor, a magnetic field is notproduced in the stator winding 22, so that the rotor 10 cannot bemaintained at a desired position. For example, if power supply isstopped on the condition that the rotor 10 is located at the desiredposition by supplying the power to the stator winding 22 (FIG. 12A), therotor 10 moves and stops at the position shifted from the desiredposition (FIG. 12B). This operation will specifically be describedbelow. The electromagnet portion 24 that generates a magnetic field bysupplying a current to the windings of the stator 22 is magnetized bythe magnetic force of the rotor 10 when the supply of the current to thestator winding 22 is stopped. Therefore, attraction force is generatedbetween the electromagnet portion 24 and the rotor (magnet) 10 so thatthe rotor 10 moves to a specific position (stable point). Specifically,as shown in FIG. 12A, the adjacent electromagnet portions 24 that aremagnetized with a predetermined ratio are uniformly magnetized by themagnetic force of the magnet of the rotor 10 when the supply of thecurrent to the stator winding 22 is stopped. Accordingly, the rotor 10stops at the middle position between the adjacent electromagnet portions24 as shown in FIG. 12B. This stop position is the stable point.

FIGS. 13A and 13B are views showing the configuration of a driver thatdrives a focus lens by the stepping motor. As shown in FIG. 13A, whenthe power is supplied to the stepping motor 33 that drives the focuslens 31 (when excitation ON), the focus lens 31 is stopped at a desiredstop position. On the other hand, when no power is supplied to thestepping motor 33 (when excitation OFF), the focus lens 31 is stopped ata position shifted from the desired stop position as shown in FIG. 13B.Accordingly, for the motor described above, precision in a stop positionof the lens is degraded when no power is supplied to the motor.

SUMMARY

In a general compact-type digital camera, the high precision for a stopposition of a focus lens is required during still image shooting, andtherefore the excitation is turned ON. On the other hand, in the casesother than the shooting of a still image, precision for the stopposition of the focus lens is not so required, and thus the excitationis turned OFF. As described above, in a compact digital camera, thesupply of power to a drive member is stopped when the precision for thestop position of the focus lens is unnecessary, resulting in powersaving.

However, even in such a digital camera, high precision for the stopposition of the focus lens may be required during moving image shooting.For example, it may be required when the depth of field is shallow when,for example, the zoom lens is driven to a telephoto side and a diaphragmis driven to an open side. In this case, when the precision for the stopposition of the focus lens is poor, a subject is not in focus and anout-of-focus moving image might be captured.

Further, in the cases other than the shooting of a moving image, theremay be the case in which high precision for the stop position of thefocus lens is required. For example, it is the case (in live view mode)in which the digital camera displays an image of data generated by animaging device on a liquid crystal monitor as a through-the-lens image.In this case, an out-of-focus moving image might also be captured andthus an out-of-focus through image might be displayed, similarly.

Further in a digital camera system including an interchangeable lens anda camera body, the problem described above may be likely to occurbecause the depth of field can be made shallower in the interchangeablelens than that in a compact-type digital camera.

In order to solve the above-mentioned problem, an imaging apparatus isprovided that can reduce power consumption of the imaging apparatus andprecisely hold a focused state of a subject as required.

In a first aspect of the present invention, an imaging apparatusincluding the following configuration is provided. The imaging apparatusincludes an optical system including a focus lens; a driver configuredto drive the focus lens; a controller configured to control a supply ofpower to the driver; and a setting unit configured to set a power supplymode for specifying a method of supplying power to the driver. When apredetermined power supply mode is set, the controller determinesaccording to a magnitude of a depth of field of the optical systemduring whether holding power for holding the state of the focus lens issupplied to the driver when the focus lens is stopped, and controls thesupply of the holding power to the driver according to the result of thedetermination.

According to this configuration, when the imaging apparatus allows thefocus lens to stop and stand by in case where the imaging apparatus isset to a predetermined mode, e.g., a power-saving mode, it can becontrolled such that a holding power is to be supplied or not to thedrive means according to the depth of field.

In a second aspect, a camera system including an interchangeable lensand a camera body. The camera body includes a power supplying unitconfigured to supply power to the interchangeable lens; a setting unitconfigured to set a power supply mode for specifying a method ofsupplying power; and a sending unit configured to send settinginformation indicating the set power supply mode to the interchangeablelens. The interchangeable lens includes an optical system including afocus lens; a driver configured to drive the focus lens with the powerreceived from the power supplying unit; and a controller configured tocontrol a supply of power to the driver. When a predetermined powersupply mode is set according to the setting information from the camerabody, the controller determines according to a magnitude of a depth offield of the optical system whether holding power for holding the stateof the focus lens is supplied to the driver when the focus lens isstopped, and controls the supply of the holding power to the driveraccording to the result of the determination.

In a third aspect, an interchangeable lens mountable to a camera bodyincludes: an optical system including a focus lens; a driver configuredto drive the focus lens with power received from the camera body; acontroller configured to control a supply of power to the driver; and asetting unit configured to set a power supply mode for specifying amethod of supplying power to the driver under the control of the camerabody. When a predetermined power supply mode is set according to settinginformation from the camera body, the controller determines according toa magnitude of a depth of field of the optical system whether holdingpower for holding the state of the focus lens is supplied to the driverwhen the focus lens is stopped, and controls the supply of the holdingpower to the driver according to the result of the determination.

The imaging apparatus in the above described aspects determines whetherthe holding power should be supplied to the driver according to theinformation relating to the depth of field of the optical system, andthen supplies the holding power to the drive unit, with the imagingapparatus set to a predetermined mode in which the focus lens is stoppedand stands by. This configuration allows power consumption in theimaging apparatus to be reduced, and further the focused state to asubject to be held precisely as needed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a digital camera according to a firstembodiment.

FIG. 2 is a block diagram showing an example of a configuration of thedigital camera according to the first embodiment.

FIG. 3A is a diagram for explaining setting information sent accordingto a control mode or a control state of a camera body according to thefirst embodiment.

FIG. 3B is a diagram for explaining power setting that is set accordingto the control state of a camera system.

FIG. 4 is a diagram for explaining determination as to whether holdingpower should be supplied to a focus driver according to the settinginformation acquired by an interchangeable lens in the first embodiment.

FIG. 5 is a diagram for explaining determination as to whether holdingpower should be supplied to a focus driver according to the informationrelating to the depth of field in an embodiment.

FIG. 6 is a flowchart for explaining an example of an operation of thecamera body in the embodiment.

FIG. 7 is a flowchart for explaining an example of an operation of theinterchangeable lens in the embodiment.

FIG. 8A is a diagram for explaining a supply of power to the focus lensdriver during holding-power-ON-setting, and FIG. 8B is a diagram forexplaining a supply of power to the focus lens driver duringholding-power-OFF-setting.

FIG. 9 is a flowchart for explaining an example of an operation of theinterchangeable lens in the embodiment.

FIG. 10 is a flowchart for explaining an example of an operation of theinterchangeable lens in the embodiment.

FIG. 11 is a flowchart for explaining an example of an operation of acamera body in another embodiment.

FIG. 12A is a view for explaining an internal condition of a steppingmotor to which holding power is supplied, and FIG. 12B is a view forexplaining an internal condition of a stepping motor to which no holdingpower is supplied.

FIG. 13A is a view for explaining a stop position of a focus lens whenholding power is supplied to the stepping motor, and FIG. 13B is a viewfor explaining the stop position of the focus lens when no holding poweris supplied to the stepping motor.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments will be described below with reference to the drawings.

First Embodiment 1. Structure 1-1. Outline of Overall Structure

FIG. 1 is a perspective view of a digital camera according to anembodiment. FIG. 2 is a diagram showing a hardware configuration of thedigital camera according to the embodiment.

[0020] The digital camera 1 according to the present embodiment includesa camera body 2 and an interchangeable lens 3 that is mountable to thecamera body 2.

The camera body 2 includes a CMOS sensor 201, a mechanical shutter 202,a signal processing processor (DSP) 203, a buffer memory 204, a liquidcrystal monitor 205, an electronic viewfinder (EVF) 206, a power source207, a body mount 208, a flash memory 209, a card slot 210, a CPU 211, ashutter switch 212, an electronic flash 213, a microphone 214, and aspeaker 215.

The interchangeable lens 3 includes a lens mount 301, an optical systemincluding a zoom lens 303, a focus lens 304, and an OIS lens 305, afocus driver 306 that drives the focus lens 304, an OIS driver 320 thatdrives the OIS lens 305, a diaphragm 307, an diaphragm driver 308 thatdrives the diaphragm 307, a zoom ring 309, a focus ring 310, a lenscontroller 311, a buffer memory 312, a zoom lens position detector 313,a flash memory 314, and a gyro sensor 330.

1-2. Configuration of Camera Body

The camera body 2 is configured to capture a subject image collected bythe optical system of the interchangeable lens 3 and record the capturedimage data in a recording medium.

The CMOS sensor 201 includes a light-receiving element, an AGC (gaincontrol amplifier), and an AD converter. The light-receiving elementconverts an optical signal collected by the optical system to anelectric signal to generate image data. The AGC amplifies the electricsignal outputted from the CMOS sensor 201. The AD converter converts theelectric signal outputted from the CMOS sensor 201 to a digital signal.The CMOS sensor 201 performs various operations, such as an exposure,transfer, electronic shutter, or the like, according to a control signalreceived from the CPU 211. These various operations can be realized by atiming generator or the like.

The mechanical shutter 202 switches transmission and cutoff of theoptical signal input to the CMOS sensor 201 through the optical system.The mechanical shutter 202 is driven by a mechanical shutter driver. Themechanical shutter driver includes components such as a motor, spring,or the like. The mechanical shutter driver drives the mechanical shutter202 under the control of the CPU 211. Specifically, the mechanicalshutter 202 opens or closes to temporarily adjust amount of lightreaching the CMOS sensor 201.

The signal processing processor (DSP) 203 performs a predetermined imageprocess to the image data that is converted to the digital signal by theAD converter. The predetermined image process includes, for example, agamma conversion, YC conversion, electronic zoom process, compressionprocess, extension process, or the like, but the image process is notlimited thereto.

The buffer memory 204 serves as a work memory when the signal processingprocessor 203 performs a process or when the CPU 211 performs thecontrol process. The buffer memory 204 can be realized by a DRAM, forexample.

The liquid crystal monitor 205 is disposed at the backside of the camerabody 2 and can display the image data generated by the CMOS sensor 201or image data obtained by a predetermined process to the image data. Theimage signal inputted into the liquid crystal monitor 205 is convertedto an analog signal from the digital signal by a DA converter, when theimage signal is outputted to the liquid crystal monitor 205 from thesignal processing processor 203.

The electronic viewfinder 206 is disposed within the camera body 2, andcan display the image data generated by the CMOS sensor 201 or imagedata obtained by applying a predetermined process to the image data. Animage signal inputted to the electronic viewfinder 206 is similarlyconverted to an analog signal from the digital signal by the DAconverter, when the image signal is outputted to the electronicviewfinder 206 from the signal processing processor 203.

To display an image, the liquid crystal monitor 205 and the electronicviewfinder 206 are switched by a display switching unit 217.Specifically, while an image is displayed on the liquid crystal monitor205, no image is displayed on the electronic viewfinder 206. While animage is displayed on the electronic viewfinder 206, no image isdisplayed on the liquid crystal monitor 205. The display switching unit217 can be realized by a physical structure such as a selection switch.For example, when the signal processing processor 203 and the liquidcrystal monitor 205 are electrically connected to each other, theelectrical connection between the signal processing processor 203 andthe liquid crystal monitor 205 is disconnected so that the signalprocessing processor 203 and the electronic viewfinder 206 areelectrically connected through the switch of the changeover switch. Thedisplay switching unit 217 is not limited to the above-mentionedstructure. The display switching unit 217 may change the display on theliquid crystal monitor 205 and the display on the electronic viewfinder206 based on the control signal from the CPU 211.

As described above, the display on the liquid crystal monitor and thedisplay on the electronic viewfinder are switched. It is to be notedthat this switching is done because of the structural limitation.Therefore, display may be provided on the liquid crystal monitor and theelectronic viewfinder simultaneously. When an image is simultaneouslydisplayed, the image displayed on the liquid crystal monitor and theimage displayed on the electronic viewfinder may be the same or may bedifferent.

The power source 207 supplies power consumed by the digital camera 1.The power source 207 may be a dry battery or a rechargeable battery.Further, the power source 207 may supply power, which is externallysupplied through a cord, to the digital camera 1.

The body mount 208 cooperating with the lens mount 301 of theinterchangeable lens 3 is a member that enables attachment/detachmentto/from the interchangeable lens 3. The body mount 208 can beelectrically connected to the interchangeable lens 3 by means of aconnection terminal or the like. Further, the body mount 208 can bemechanically connected by means of a mechanical member such as aengaging member. The body mount 208 can output a signal from the lenscontroller 311 in the interchangeable lens 3 to the CPU 211, and canoutput a signal from the CPU 211 to the lens controller 311 of theinterchangeable lens 3. Specifically, the CPU 211 can send and receivethe control signal or information relating to optical system to and fromthe lens controller 311 in the interchangeable lens 3. The body mount208 further supplies power which is supplied from the power source 207to the lens controller 311. In this manner, the body mount 208 suppliespower consumed in the interchangeable lens 3.

The flash memory 209 is a storage medium used as an internal memory. Theflash memory 209 can store image data or image data obtained byperforming a predetermined process to original image data. The flashmemory 209 can also store a digitalized voice signal. The flash memory209 can also store a program or a setting value for the control of theCPU 211 in addition to the image data or the voice signal.

The card slot 210 is a slot through which a memory card 218 serving as astorage medium is detachably inserted. The memory card 218 can storeimage data or image data obtained by performing a predetermined processto original image data. The memory card 218 can also store a digitalizedvoice signal.

The CPU 211 controls the overall of the camera body 2. The CPU 211 maybe realized by a microcomputer or a hard-wired circuit. Specifically,the CPU 211 performs various controls. The various controls will bedescribed in detail in Section 2-1.

The shutter switch 212 is a button provided on the top surface of thecamera body 2 and detects a half-press or a full-press operations by auser. When the shutter switch 212 detects the half-press operation by auser, the shutter switch 212 outputs a half-press signal to the CPU 211.On the other hand, when the shutter switch 212 detects the full-pressoperation by the user, the shutter switch 212 outputs a full-presssignal to the CPU 211. The CPU 211 performs various controls based onthese signals. In the present embodiment, the full-press signal means ashooting start signal.

The electronic flash 213 irradiates a subject with light based on thecontrol signal from the CPU 211. For example, the electronic flash 213can be composed of a xenon lamp and a capacitor and others. When theelectronic flash 213 is configured as described above, the electronicflash 213 accumulates high-voltage charges into the capacitor andapplies these charges to an electrode of the xenon lamp, whereby itradiates light.

The microphone 214 converts voice into an electric signal. The electricsignal outputted from the microphone 214 is converted to a digitalsignal by the AD converter. The digital signal converted by the ADconverter is stored in the flash memory 209 or the memory card 218 underthe control of the CPU 211.

The speaker 215 converts an electric signal into voice. The electricsignal inputted to the speaker 215 is a signal converted by the DAconverter from the digital signal to the electric signal. The digitalsignal read out from the flash memory 209 or the memory card 218 isoutputted to the DA converter under the control of the CPU 211.

A mode switching dial 221 is an operation member mounted at the outsideof the camera body 2. The mode switching dial 221 is configured into asubstantially circular shape. The mode switching dial 221 can select onecontrol mode among a plurality of control modes through a turningoperation by a user. Specifically, the mode switching dial 221 candetect the control mode, which is moved to a predetermined position, soas to select one of the plurality of control modes. The plurality ofcontrol modes include, for example, a “still image shooting mode”, a“moving image shooting mode”, and a “playback mode”. When an indicationshowing the “still image shooting mode” provided on the top surface ofthe mode switching dial is moved to a predetermined position (selectionposition), the mode switching dial 221 outputs a mode switching signalwhich indicates that the mode is changed to the “still image shootingmode”, to the CPU 211. Thus, the changeover of the control mode can bedetected.

1-3. Configuration of Interchangeable Lens

The optical system includes the zoom lens 303, the focus lens 304, theOIS lens 305, and an objective lens 302, collecting light from asubject. The zoom lens 303 is driven by the zoom ring 309 so as toadjust a zoom magnification. The focus lens 304 is driven by the focusdriver 306 or the focus ring 310 so as to adjust a focus. The OIS lens305 is driven by an OIS driver 320. The focus lens 304, the zoom lens303, and the OIS lens 305 are movable lenses.

The OIS lens 305 is movable in a plane vertical to an optical axis ofthe optical system. The optical axis of the optical system can be bentthrough the movement of the OIS lens 305 in the plane vertical to theoptical axis of the optical system. When the OIS lens 305 is moved inthe direction in which a shake of the digital camera 1 detected by thelater-described OIS driver 320 is canceled, an image blur caused by theshake of the digital camera 1 can be prevented.

The focus driver 306 drives the focus lens 304 under the control of thelens controller 311. The present embodiment illustrates that the focusdriver 306 is realized by a stepping motor and a driver. The focusdriver 306 is configured such that power is supplied from the lenscontroller 311 so as to drive the focus lens 304. When power is suppliedfrom the lens controller 311, the focus driver 306 stops the focus lens304 at a desired position. On the contrary, when power is not suppliedfrom the lens controller 311, the focus driver 306 stops the focus lens304 at a position with precision lower than that at the desiredposition. In summary, the focus driver 306 stops the focus lens 304 atthe different positions for holding the focus lens 304 where theprecisions are different between the case in which power is suppliedfrom the lens controller 311 and the case in which no power is suppliedfrom the lens controller 311. When power is supplied, the focus driver306 can stop the focus lens 304 at the desired position more precisely(with higher precision) compared to the case in which no power issupplied.

The focus driver 306 stops the focus lens 304 at a desired position whenpower is supplied. However, it is unnecessary to stop the focus lens 304at an exact position. Specifically, the focus driver 306 may stop thefocus lens 304 with precision higher than the precision at the positionwhere the focus lens 304 is stopped when no power is supplied from thelens controller 311.

The OIS driver 320 drives the OIS lens 305 under the control of the lenscontroller 311 based on the output from the gyro sensor 330. An opticalimage blur correction function can be realized by the gyro sensor 330,the lens controller 311, the OIS driver 320 and the OIS lens 305. Thegyro sensor 330 detects a moving angular speed of the digital camera 1.The lens controller 311 integrates the angular speed detected by the OISdriver 320 so as to calculate the angular speed of the digital camera 1.This results in shake amount of the digital camera 1. The lenscontroller 311 gives an instruction to the OIS driver 320 for drivingthe OIS lens 305 so that the movement of the digital camera 1 iscancelled and a subject image does not move on the CMOS sensor 201 asmuch as possible. The OIS driver 320 drives the OIS lens 305 accordingto this instruction. As described above, the OIS lens 305 moves in thevertical plane of the optical axis of the optical system to bend theoptical axis of the optical system. This allows motion of the subjectimage on the CMOS sensor 201 to be suppressed as much as possible.

The diaphragm 307 regulates quantity of light passing through theoptical system. For example, light can be regulated by increasing ordecreasing an opening made by five blades.

The diaphragm driver 308 changes the size of the opening of thediaphragm 307. In the first embodiment, the diaphragm driver 308 changesthe size of the opening of the diaphragm 307 under the control of thelens controller 311. The size of the opening can be designated by an Fvalue. The diaphragm driver 308 drives the diaphragm 307 under thecontrol of the lens controller 311, but it is not limited thereto. Thediaphragm driver 308 may drive the diaphragm 307 with a mechanicalmethod.

The diaphragm driver 308 includes an encoder that detects the size(position) of the opening of the diaphragm and outputs the result as anAV (Aperture Value) (information relating to brightness). The diaphragmdriver 308 outputs the AV to the lens controller 311. The AV outputtedfrom the diaphragm driver 308 ranges AV0 to AV5, for example.

The zoom ring 309 is provided at the outside of the interchangeable lens3 for driving the zoom lens 303 according to the operation by a user.The zoom ring 309 mechanically drives the zoom lens 303, when turned bythe user.

The focus ring 310 is provided at the outside of the interchangeablelens 3 for driving the focus lens 304 according to the operation by auser. When turned by a user, the focus ring 310 detects the user'soperation with a sliding resistance to output a signal relating to theoperation to the lens controller 311. The lens controller 311 controlsthe focus driver 306 according to the signal relating to the inputtedoperation. Thus, the focus driver 306 drives the focus lens 304.

The lens controller 311 controls the entire interchangeable lens 3. Thelens controller 311 may be realized by a microcomputer or by ahard-wired circuit. Specifically, the lens controller 311 performsvarious controls. The various controls by the lens controller 311 willbe described in Section 2-2.

The buffer memory 312 functions as a work memory, when the lenscontroller 311 performs control processes. The buffer memory 312 can berealized by a DRAM, for example.

The flash memory 314 is electrically connected to the lens controller311. The flash memory 314 can store a control program, a parameter orthe like.

The zoom lens position detector 313 acquires information relating to thezoom position of the zoom lens 303. Specifically, the zoom positionindicates the position of the zoom lens 303 designated for every region,which is formed by dividing the movable range of the zoom lens 303 inplural regions. The lens controller 311 periodically acquires theinformation relating to the zoom position detected by the zoom lensposition detector 313.

The zoom lens position detector 313 is composed of a sliding resistanceand others. The zoom lens position detector 313 detects the informationrelating to the zoom position of the zoom lens 303 in terms of a voltagevalue. Since the lens controller 311 periodically reads the voltagevalue detected by the zoom lens position detector 313 and performsAD-conversion to the voltage value to acquire the information(digitalized data) relating to the zoom position divided into 256. It isnoted in the present embodiment, the information relating to the zoomposition divided into 6 is used for simplifying the description.

1-4. Correspondence of Terms

The digital camera 1 is one example of an imaging apparatus or a camerasystem. The focus driver 306 is one example of a drive unit. The CPU 211and the lens controller 311 are one examples of a setting unit and acontroller. The power source 207 is one example of a supplying unit. Thecombination of the CPU 211 and the body mount 208 is one example of asending unit.

2. Control of Camera Body and Interchangeable Lens

The control of the camera system thus configured will be described belowin detail.

2-1. Control of CPU in Camera Body

The camera system 1 in the present embodiment can be set to a movingimage shooting mode for shooting a moving image, a still image shootingmode for shooting a still image, and a playback mode for reproducing animage, as a control mode. Power setting modes set to the interchangeablelens 3 include a normal mode, and a power-saving mode for reducing powerconsumption more than in the normal mode. FIG. 3A shows the relationshipbetween the control modes set to the camera body 2 and the power settingin the respective control modes. In the normal mode, even if the focuslens 304 is not driven, the supply of the power to the focus driver 306is continued. On the other hand, in the power-saving mode, when thefocus driver 304 is not driven, the supply of the power to the focusdriver 306 is stopped so that the power is saved.

The CPU 211 in the camera body 2 determines whether it is necessary toset the interchangeable lens 3 to the power-saving mode according to thecontrol mode set to the camera body 2, based on the relationship shownin FIG. 3A. For example, when the CPU 211 determines that it isnecessary to set the interchangeable lens 3 to the power-saving mode,the CPU 211 sends control information for controlling theinterchangeable lens 3 to the power-saving mode to the interchangeablelens 3.

The control mode is selected by a user by means of the mode switchingdial 221. When the mode selected by the mode switching dial 221 is themoving image shooting mode or the playback mode, the CPU 211 determinesthat it is necessary to set the interchangeable lens 3 to thepower-saving mode. This is because the moving image shooting mode or theplayback mode does not require the precision of the position where thefocus lens is stopped, compared to the still image shooting mode. On theother hand, when the mode selected by the mode switching dial 221 is thestill image shooting mode, the CPU 211 determines that it is necessaryto set the interchangeable lens 3 to the normal mode.

The CPU 211 sends setting information which indicates whether theinterchangeable lens 3 needs to be set to the power-saving mode, to thelens controller 311 as described above. Specifically, the CPU 211 sendssetting information indicating the power-saving mode to the lenscontroller 311, when it determines that it is necessary to set theinterchangeable lens 3 to the power-saving mode. On the other hand, whenthe CPU 211 determines that it is unnecessary to set the interchangeablelens 3 to the power-saving mode, it sends setting information indicatingthe normal mode to the lens controller 311. The lens controller 311performs a power control according to the setting information.

2-2. Control of Lens Controller in Interchangeable Lens

In the interchangeable lens 3, the lens controller 311 receives thesetting information indicating the power-saving mode or the normal modefrom the CPU 211. The lens controller 311 sets the interchangeable lens3 to the power-saving mode or the normal mode according to the receivedsetting information.

The lens controller 311 also determines whether power for holding theposition of the focus lens 304 (hereinafter referred to as “holdingpower”) is supplied to the focus driver 306 according to the powersetting (normal mode) as shown in FIG. 4.

Specifically, when the normal mode is set, the lens controller 311supplies the holding power for holding the position of the focus lens304 to the focus driver 306. On the other hand, when the power-savingmode is set, the lens controller 311 determines according to the depthof field of the optical system whether the holding power is supplied tothe focus driver 306 in order to hold the focus lens 304 at the positionwhere it is stopped.

When the lens controller 311 determines that it supplies the holdingpower to the focus driver 306, the lens controller 311 supplies theholding power to stop the focus lens 304 and hold it at the stopposition, to the focus driver 306. In this case, the lens controller 311supplies the power supplied from the body mount 208 to the focus driver306 as the holding power.

The control of the lens controller 311 will specifically be described.When the lens controller 311 receives setting information indicating thepower-saving mode or the normal mode from the CPU 211 in the camera body2, it stores the setting information in the buffer memory 312. The lenscontroller 311 sets the interchangeable lens 3 to the power-saving modeor to the normal mode according to the received setting information.

When the setting information stored in the buffer memory 312 indicatesthe normal mode, the lens controller 311 supplies the holding power tothe focus driver 306. On the other hand, when the setting informationstored in the buffer memory 312 indicates the power-saving mode, thelens controller 311 determines the supply/stop of the holding power,taking the depth of field of the optical system into consideration. Whenthe depth of field is deep, less influence is given to the focus stateeven if the stop position of the focus lens 304 is somewhat shifted dueto the non-supply of the holding power, so that there is no influence onan image quality. However, when the depth of field is shallow, the focusstate is broken soon after the stop position of the focus lens 304 isshifted due to the non-supply of the holding power, with the result thatthe image quality is deteriorated. As described above, when the depth offield is deep, there is no problem even when the holding power is notsupplied. However when the depth of field is shallow, the image qualitymight be deteriorated if the holding power is not supplied. In view ofthis, whether the holding power is supplied or stopped is determinedconsidering the depth of field, in the present embodiment.

Specifically, the lens controller 311 acquires, as information relatingto the depth of field of the optical system, information relating to thezoom position of the zoom lens 303 and AV (aperture value) of thediaphragm 307. The information relating to the zoom position can beacquired based on the information outputted from the zoom lens positiondetector 313. The AV can be acquired based on the information outputtedfrom the diaphragm driver 308. The depth of field is obtained accordingto the zoom position of the zoom lens 303 and the AV of the diaphragm307. Whether the holding power is supplied (ON) or stopped (OFF) isdetermined for the obtained depth of field. FIG. 5 shows tableinformation indicating the relationship among the zoom position of thezoom lens 303 and the AV of the diaphragm 307, and the supply (ON)/stop(OFF) of the holding power.

The lens controller 311 refers to the table information shown in FIG. 5and determines whether the holding power is supplied or not to the focusdriver 306 based on the acquired information. For example, when the zoomposition is “3” and the AV is “2” (when the depth of field is shallow),the lens controller 311 determines that the excitation becomes “ON” andthe holding power is supplied to the focus driver 306.

When the lens controller 311 determines that the holding power issupplied to the focus driver 306, it supplies the holding power to thefocus lens 304 when it allows the focus lens 304 to stand by at the stopposition. On the other hand, when the lens controller 311 determinesthat the holding power is not supplied to the focus driver 306, it doesnot supply the holding power to the focus lens 304 when it allows thefocus lens 304 to stand by at the stop position. The case in which theholding power is not supplied to the focus lens 304 means that thecontinuous supply of the holding power is stopped. That is, the lenscontroller 311 may supply temporal holding power during the period whenthe focus lens 304 is in its stand-by state after it is stopped.

3. Operation

The operation of the digital camera 1 thus configured will be describedwith reference to the flowcharts shown in FIGS. 6 to 9. In thedescription below, it is supposed that the interchangeable lens 3 isattached to the camera body 2. When the power is turned ON, the camerabody 2 starts the operation described below.

The operation of the camera body 2 will firstly be described withreference to the flowchart shown in FIG. 6.

When the power of the camera body 2 is turned ON or the control mode ischanged (S11), the CPU 211 determines whether or not the control mode isset to the moving image shooting mode or the playback mode (S12). Whenthe power of the camera body 2 is turned ON, the CPU 211 detects thecontrol mode selected by the mode switching dial 221. Then, the CPU 211stores information relating to the control mode detected by the modeswitching dial 221 in the buffer memory 204. Thus, the CPU 211 cancontrol components of the camera body 2 according to the storedinformation relating to the control mode.

Returning to FIG. 6, when the CPU 211 determines in step S12 that thecontrol mode is set to the moving image shooting mode or the playbackmode, it sends the setting information indicating the power-saving modeto the lens controller 311 (S13). On the other hand, when determining atstep S12 that neither the moving image shooting mode nor the playbackmode is set, the CPU 211 sends the setting information indicating thenormal mode to the lens controller 311 (S14).

After that, when the control mode is changed through the mode switchingdial 221, the process described above is repeated.

Next, the operation of the interchangeable lens 3 will be described withreference to the flowcharts shown in FIGS. 7 and 8. The lens controller311 determines whether the setting information indicating thepower-saving mode or the normal mode is acquired (S21).

When receiving the setting information, the lens controller 311 allowsthe buffer memory 312 to store the setting information (S22).Thereafter, the lens controller 311 determines whether the receivedsetting information indicates the power-saving mode (S23).

When the received setting information indicates the power-saving mode,the lens controller 311 determines according to the information relatingto the depth of field of the optical system whether the holding power issupplied to the focus driver 306 (S24). The specific method for thisdetermination is as described previously with reference to the table inFIG. 5. When determining that the holding power is supplied, the lenscontroller 311 sets up a setting for operation to supply the holdingpower to the focus driver 306 after the focus lens 304 is driven(hereinafter referred to as “holding-power-ON-setting”) (S25). On theother hand, when determining that the holding power is not supplied, thelens controller 311 sets up a setting for operation to supply no holdingpower to the focus driver 306 after the focus lens 304 is driven(hereinafter referred to as “holding-power-OFF-setting”) (S26).

On the other hand, when the received setting information indicates thenormal mode at step S23, the lens controller 311 sets up a setting foroperation to supply the holding power to the focus driver 306 after thefocus lens 304 is driven (holding-power-ON-setting) (S27).

FIGS. 8A and 8B are diagrams for explaining the power supplied to thefocus driver 306 when the holding-power-ON-setting and theholding-power-OFF-setting are performed. When theholding-power-ON-setting is set, the holding power is being supplied tothe focus driver 306 not only while the focus lens 304 is driven butalso while the focus lens 304 stands by at the stop position after thefocus lens 304 is driven, as shown in FIG. 8A. On the other hand, whenthe holding-power-OFF-setting is set, the power is not supplied to thefocus driver 306 while the focus lens 304 stands by at its stop positionafter it is driven, as shown in FIG. 8B. Specifically, the power issupplied only when the focus lens 304 is driven.

The operation when the holding-power-ON-setting or theholding-power-OFF-setting is set will be described with reference to theflowchart shown in FIG. 9.

Firstly, the lens controller 311 determines whether the focus lens 304needs to be driven or not (S31). The case in which the focus lens needsto be driven is, for example, a case in which a zoom tracking isrequired in the interchangeable lens 3, or a case in which the focuslens 304 needs to be driven according to the control signal from thecamera body 2.

When determining that the focus lens 304 needs to be driven, the lenscontroller 311 supplies driving power to the focus driver 306 so as todrive the focus lens 304 (S32). The driving power may be suppliedcontinuously following the holding power while the holding power issupplied. Although the driving power and the holding power aredistinctively described for clarifying the description, it isunnecessary to distinguish them.

After the driving of the focus driver 306 is completed, the lenscontroller 311 determines whether the holding-power-ON-setting is set(S33). When the holding-power-ON-setting is set, the lens controller 311supplies the holding power to the focus driver 306 (S34). The supply ofthe holding power allows the focus driver 306 to stop the focus lens 304at the desired position. On the other hand, when theholding-power-OFF-setting is set, the lens controller 311 does notsupply the holding power to the focus driver 306 (S35). When the holdingpower is not supplied, the focus driver 306 might stop the focus lens304 at the position shifted from the desired position.

When a series of processes described above is completed, the lenscontroller 311 returns to step S31 to perform the same processessubsequently.

When the zoom lens 303 or the diaphragm 307 is driven in the camerasystem 1, the depth of field of the optical system is changed. In thiscase, it is preferable that the operation shown in the flowchart in FIG.10 is performed in the interchangeable lens 3 considering the depth offield.

When detecting that the zoom lens 303 or the diaphragm 307 is adjusted(S41), the lens controller 311 reads the setting information stored inthe buffer memory 312 and determines whether the power-saving mode isset (S42). When determining that the power-saving mode is set, the lenscontroller 311 performs the process at step S43. When determining thatthe power-saving mode is not set, the lens controller 311 returns to theprocess at step S41.

At step S43, the lens controller 311 acquires, as the informationrelating to the depth of field, the information relating to the zoomposition based on the information outputted from the zoom lens positiondetector 313 and the AV (aperture value) based on the informationoutputted from the diaphragm driver 308. These pieces of the acquiredinformation are based on the information outputted after the zoom lens303 or the diaphragm driver 308 is adjusted. The lens controller 311then refers to the table information in FIG. 5 based on the zoomposition and the AV (depth of field) to determine whether it isnecessary to supply the holding power (S44). When determining that it isnecessary to supply the holding power, the lens controller 311 sets up asetting (holding-power-ON-setting) for operation to supply the holdingpower to the focus driver 306 (S45). On the other hand, when determiningthat no holding power is supplied, the lens controller 311 sets up asetting (holding-power-OFF-setting) for operation to supply no holdingpower to the focus driver 306 (S46).

According to the configuration described above, the interchangeable lens3 itself can determine whether it is necessary to supply the holdingpower. Therefore, the camera body 2 can reduce power consumption in theinterchangeable lens 3 while keeping the focused state to the subjectonly by sending the information relating to the power-saving mode.

4. Conclusion

The digital camera 1 includes the camera body 2 and the interchangeablelens 3 that is mountable to the camera body 2. The camera body 2includes the CPU 211 sending the instruction to the interchangeable lens3. The interchangeable lens 3 includes the optical system having thefocus lens 304, the focus driver 306 that drives the focus lens 304, thelens controller 311 that can set the lens to the power-saving modeaccording to the instruction from the camera body 2, the lens controller311 that determines whether the holding power for allowing the focuslens 304 to stop and stand by is supplied to the focus driver 306according to the information relating to the depth of field of theoptical system when the power-saving mode is set by the lens controller311 and the focus lens 304 is controlled to stop and stand by, and thelens controller 311 that supplies the holding power to the focus driver306 according to the result of the determination of itself.

According to the configuration, when the power-saving mode is set andthe focus lens is held at the stop position, it can be determinedaccording to the depth of field whether the holding power is supplied tothe focus driver. Accordingly, it is controlled such that, when thedepth of field is shallow, the holding power is supplied to the focusdriver, while the holding power is not supplied to the focus driver whenthe depth of field is deep. Accordingly, when the depth of field isshallow, the priority is given to keep the focused state to the subjectso that the deterioration in the image quality can be prevented. On theother hand, when the depth of field is deep, the priority is given tothe reduction in power consumption so that power-saving is achieved.

Other Embodiments

The first embodiment has been described above. However, an embodiment isnot limited to the above-mentioned embodiment, and can be realized byother embodiments. The other embodiments will be described collectivelyas follows.

In the above-mentioned embodiment, the imaging device is made of a CMOSsensor. However, the imaging device is not limited thereto. For example,the imaging device may be made of a CCD image sensor. Specifically, theimaging device can take any configurations so long as it captures asubject image to generate image data (digital signal or electricsignal). When the imaging device is made of the CMOS sensor, powerconsumption can be reduced.

The CPU 211 in the above-mentioned embodiment determines whether it isnecessary to set the interchangeable lens 3 to the power-saving mode,according to the control mode set to the camera body 2. However, theembodiment is not limited thereto. It may also be determined whether itis necessary to set the interchangeable lens 3 to the power-saving modeconsidering the control state (operation state) of the camera body 2.For example, when the mode selected by the mode switching dial 221 isthe still image shooting mode, the CPU 211 may determine whether it isnecessary to set the interchangeable lens 3 to the power-saving mode,according to whether the shutter switch 212 is kept to be half-pressed(see FIG. 3B). When the shutter switch 212 is kept to be half-pressed,the CPU 211 determines that it is unnecessary to set the interchangeablelens 3 to the power-saving mode. This is because, when the shutterswitch 212 is half-pressed in the still image shooting mode, the digitalcamera 1 starts preparation for starting the shooting. Specifically, inthe preparation for starting the shooting, automatic focus control isgenerally performed and thus high precision of the stop position of thefocus lens is required. When the shutter switch 212 is not half-pressed,the CPU 211 determines that the interchangeable lens 3 needs to be setto the power-saving mode. This allows the power consumption to bereduced.

The specific operation of the camera body 2 will be described withreference to the flowchart shown in FIG. 11. When the still imageshooting mode is set, the CPU 211 sends the setting informationindicating the power-saving mode to the lens controller 311 (S51).Thereafter, the CPU 211 determines whether the shutter switch 212 ishalf-pressed (S52). When the shutter switch 212 is half-pressed, the CPU211 sends the setting information indicating the normal mode to the lenscontroller 311 (S53). Then, the CPU 211 determines whether thehalf-pressed state of the shutter switch 212 is released (S54). Whendetermining that the half-press state of the shutter switch 212 isreleased, the CPU 211 returns to step S51 to perform the same processdescribed above.

In the above-mentioned embodiment, with reference to the tableinformation shown in FIG. 5, the depth of field is evaluated based onthe zoom position and the AV to determine whether the holding power issupplied. However, an embodiment is not limited thereto. The informationindicating the depth of field may be calculated based on the focaldistance and a diaphragm value (aperture value) of the diaphragmaccording to the position of the zoom lens, and whether the holdingpower is supplied may be determined according to the calculatedinformation. Either one of the zoom position and the AV may be used asthe information relating to the depth of field.

The embodiment described above is explained by using the informationrelating to the zoom position corresponding to the focal distance andthe AV corresponding to the diaphragm value, as the information relatingto the depth of field. However, the embodiment is not limited thereto.Information relating to a focus position that is in focus by the focuslens or a diameter of the least circle of confusion (permissible circleof confusion), and so on may be considered as the information relatingto the depth of field.

In the embodiment described above, the driving unit is made of the focusdriver 306 including a stepping motor and a driver thereof. However, theembodiment is not limited thereto. The driving unit may have anyconfigurations so long as it allows the focus lens to stop and stand byat the position having different precision between the case in which theholding power is supplied and the case in which no holding power issupplied. Therefore, a servomotor, a synchronous motor or the like canbe used as the driving unit.

Specifically, the embodiment is not limited to the first embodimentdescribed above, but can be achieved in various configurations.

INDUSTRIAL APPLICABILITY

The embodiments described above are applicable to a digital stillcamera, a digital video camera or the like. The embodiments describedabove are also applicable to a camera system including a camera body andan interchangeable lens.

The specific embodiments have been described. However, it should beunderstood by those skilled in the art that various modifications,alterations, and other applications are possible. Accordingly, thepossible embodiment is not limited to the specific disclosure here, butcan be limited only by the scope of the appended claims. The presentapplication is related to Japanese Patent Application No. 2008-157757(filed on Jun. 17, 2008) and U.S. Provisional Patent Application No.61/053815 (filed on May 16, 2008), the entire contents of which areincorporated herein by reference.

What is claimed is:
 1. A camera system comprising an interchangeablelens and a camera body, the camera body comprising: a power supplyingunit configured to supply power to the interchangeable lens; and asending unit configured to send setting information indicating a powersupply mode for specifying a method of supplying power to theinterchangeable lens, the interchangeable lens comprising: an opticalsystem including a focus lens; and a driver configured to drive thefocus lens with the power supplied by the power supplying unit, whereinwhen a predetermined power supply mode is set according to the settinginformation sent from the camera body, supplying, with the powersupplied by the power supplying unit, of a holding power for holding astate of the focus lens when the focus lens is stopped is changedaccording to a magnitude of a depth of field of the optical system. 2.The camera system according to claim 1, wherein the driver has differentprecisions in position for holding the focus lens between the case inwhich the holding power is supplied and the case in which no holdingpower is supplied.
 3. The camera system according to claim 2, whereinthe driver keeps holding the focus lens at a stop position at which thefocus lens is stopped when the holding power is supplied, and holds thefocus lens at a position within a predetermined range from the stopposition when no holding power is supplied.
 4. The camera systemaccording to claim 1, wherein in a power supply mode other than thepredetermined power supply mode, the holding power is supplied to thedriver when the focus lens is stopped.
 5. The camera system according toclaim 1, wherein the optical system further includes a zoom lens and adiaphragm, and the magnitude of the depth of field is determinedaccording to the position of the zoom lens and/or the opening state ofthe diaphragm.
 6. The camera system according to claim 1, wherein thepredetermined power supply mode is a mode in which power consumption ismore reduced than that in a power supply mode other than thepredetermined power supply mode.
 7. An interchangeable lens mountable toa camera body comprising: an optical system including a focus lens; anda driver configured to drive the focus lens with power supplied by thecamera body; wherein when a predetermined power supply mode forspecifying a method of supplying power is set, supplying, with the powersupplied by the camera body, of a holding power for holding a state ofthe focus lens when the focus lens is stopped is changed according to amagnitude of a depth of field of the optical system.
 8. Theinterchangeable lens according to claim 7, wherein the driver hasdifferent precisions in position for holding the focus lens between thecase in which the holding power is supplied and the case in which noholding power is supplied.
 9. The interchangeable lens according toclaim 8, wherein the driver keeps holding the focus lens at a stopposition at which the focus lens is stopped when the holding power issupplied, and holds the focus lens at a position within a predeterminedrange from the stop position when no holding power is supplied.
 10. Theinterchangeable lens according to claim 7, wherein in a power supplymode other than the predetermined power supply mode, the holding poweris supplied to the driver when the focus lens is stopped.
 11. Theinterchangeable lens according to claim 7, wherein the optical systemfurther includes a zoom lens and a diaphragm, and the magnitude of thedepth of field is determined according to the position of the zoom lensand/or the opening state of the diaphragm.
 12. The interchangeable lensaccording to claim 7, wherein the predetermined power supply mode is amode in which power consumption is more reduced than that in a powersupply mode other than the predetermined power supply mode.